This application is a 371 national stage of PCT International Application No. PCT/CH00/00219 filed Apr. 14, 2000.
The invention relates to a flowable and settable casting compound, in particular lightweight concrete, with a binder, in particular cement, and at least one lightweight aggregate, to a prefabricated element, to a structural member that is cast in situ, and also to a process for producing structured surfaces in cast structural members and elements.
Foam glass is offered on the market in plate form or as bulk material. For the purpose of producing plates of foam glass, new glass is mixed with a range of additives, is baked in moulds and thereby foamed, is then thoroughly cooled and cut into plates. The foam-glass lumps of the bulk material are fragments of a foam-glass layer which is produced by baking, at up to about 900 degrees, an old-glass powder which has been mixed with mineral additives. The origin of the glass plays a minor role. New glass can also be used for producing the foam-glass ballast. The process for producing this foam-glass ballast is described in European Patent No. 0 292 424, for example.
Foam glass is known as an inert insulating material with relatively high compressive strength. Foam-glass ballast is employed, inter alia, for perimeter insulations, granular subbases beneath structures, as lightweight ballast for pressure-equalising layers in road construction. In this connection the low weight per unit volume and the insulating property of the foam glass are primarily utilised, but its good and stable compressibility is also utilised. Furthermore, the permeability in respect of water even of the compressed structure of the ballast is valued in particular. The permeability in respect of water is based on the large cavity cross-sections between the foam-glass lumps of practically uniform size. Thanks to the absence of fines, the permeability in respect of water an be utilised permanently without any risk of flushing out. Since the individual foam-glass lumps in the texture interlock by claw action with the sharp edges in the innumerable broken-open gas pores of the surface of the foam-glass lumps, foam-glass ballast exhibits the very steep angle of repose of about 45xc2x0. It can therefore also be employed in the domain of securing slopes.
The term xe2x80x98glassxe2x80x99 in this context is to be understood to mean a broad range of vitrified and glass-like materials, such as new glass of any composition, old glass of any origin, slag from incineration plants and also, in particular, slag from blast furnaces. It has been shown that blast-furnace slag from steelworks can be processed into foam glass in a process that consumes practically no energy. The product that is obtained thereby apparently exhibits an even higher compressive strength and a lower weight per unit volume than the foam-glass product derived from old glass which is described further below. In addition, its cost is far more favourable than that of the foam glass derived from old glass with relatively high expenditure of energy.
According to the xe2x80x9cEnzyklopxc3xa4die Naturwissenschaft und Technikxe2x80x9d, Verlag Moderne Industrie, Munich 1980, a normal concrete (normal heavy concrete) has a bulk density from 2.2 to 2.5 t/m3, a compressive strength from 16 to 60 MPa (=N/mm2) and a thermal conductance of 1.97 W/mK. In order to obtain a lower weight and a lower coefficient of thermal conduction, some of the aggregates constituted by sand, gravel or stone chippings can be replaced by various lighter aggregates with inclusions of gas, e.g. pumice stone or expanded clay, or a viscous ultra-fine mortar can be interspersed with gas bubbles. As a result, lightweight concrete is obtained. According to the aforementioned encyclopedia, lightweight concrete can be subdivided into four groups. 1st Group: dense lightweight-aggregate concrete which can be used structurally for high-rise and industrial buildings as well as bridges. Parameters: bulk density 1.4 to 1.9 t/m3; compressive strength 16 to 45 MPa (=N/mm2) and thermal conductance 0.58 to 1.38 W/mK. For this concrete, use is made of the normal concrete aggregates, but they are partially replaced by lightweight aggregates. Expanded clay and expanded slate are specified as special aggregates. The grain-structure type is closed. Foam-glass lumps are proposed in EP 0 012 114 and in JP-A-10 203836 as a further possible lightweight aggregate for a concrete pertaining to this first group.
In EP 0 012 114 a process is described for producing a foam-glass granulate from a powdered glass with pasty expanding agents which consist of organic and inorganic substances. The granulate consists of fragments of a foam-glass body and comprises 100,000 to 3 million small bubbles having approximately the same size per cm3 of granulate compound. It exhibits a compressive strength of 130 kg/cm2. In one embodiment the grains of the granulate have beaded edges. In order to obtain the beaded edges, the granulate is worked mechanically, e.g. in a device resembling a sugar-coating drum, in such a manner that the edges are crushed. The granulate that is obtained with this process is, according to the disclosure, fine-pored and very lightweight and can be used as an aggregate for lightweight concrete or as a filler for plastics.
Proceeding from known processes for producing globular foam-glass bodies that find application as filling material for lightweight mortar and from known processes for producing plate-like foam glass, in JP-A-10 203836 a process is described which is practically identical to the process according to the substantially older patent specification EP 0 292 424. With this process, according to the disclosure, a foam glass having an undefined massive form is obtained which exhibits a relative density of 0.2, a proportion of adhering water of 7% and an average grain diameter of 3 cm. The following are proposed as advantageous uses of this foam glass:
raising of the ground level in the case of a soft and weak subsoil, whereby a lateral flowing movement can be suppressed,
drainage layer, e.g. beneath tennis courts,
thermal insulation in the roof area or floor area,
weight-reducing aggregate added to concrete,
soundproofing and earthquake protection.
A second group of lightweight concrete is constituted, according to the xe2x80x9cEnzyklopxc3xa4die Naturwissenschaft und Technikxe2x80x9d, by particulate-pored lightweight aggregate concrete. The latter can be employed structurally and for thermal insulation in the form of cavity blocks, large slabs and large blocks. Parameters: bulk density 1.0 to 1.4 t/m3; compressive strength 2.5 to 8 MPa (=N/mm2) and thermal conductance 0.41 to 0.58 W/mK. Expanded clay and expanded slate, but also pumice slag, sintered ash and other aggregates are specified as aggregates for this concrete. The grain-structure type is open.
A third group is constituted by aerated concrete (gas-silicate concrete, foamed concrete), which can be employed structurally and for thermal insulation in the form of structural members for walls, roofing slabs and insulating concrete. Aerated-concrete blocks are also known. Parameters: bulk density 0.3 to 1.0 t/m3; compressive strength 0.5 to 15 MPa (=N/mm2) and thermal conductance 0.058 to 0.41 W/mK. Fine sand, fly ash and slag sand are specified as aggregates for this concrete. The grain-structure type is fine-pored.
According to the aforementioned encyclopaedia, insulating concrete, which can be employed merely for thermal insulation in the form of insulating slabs, constitutes a fourth group. Parameters: bulk density 0.3 t/m3; compressive strength inadequate for load-bearing units, and thermal conductance 0.035 to 0.35 W/mK. Kieselguhr and pearlite are specified as aggregates for this concrete.
These four concrete groups show clearly that in the case of the known types of lightweight concrete the compressive strength falls below 16 N/mm2 as soon as the coefficient of thermal conduction falls below 0.5 W/mK or the weight per unit volume falls below 1.4 t/m3. It can also be inferred that in the case of a weight per unit volume of about one tonne per cubic metre a maximum compressive strength of 15 N/mm2 and no better thermal conductance than about 0.4 W/mK are attained. A compressive strength of over 8 MPa is only attained if use is made of expanded clay or expanded slate by way pf aggregate or if aerated concrete is produced from finely ground aggregates and gas-forming additives. However, expanded clay and expanded slate utilise limited resources, and aerated concrete, for reasons of quality assurance, cannot be used for load-bearing cast-in-place concrete.
From this survey it can therefore further be gathered that there is no constructional concrete capable of being cast on the building site having a bulk density below 1.4 t/m3 and a thermal conductance below 0.58 W/mK. Aerated concrete could presumably also be cast on the building site. However, its quality depends very much on the external conditions. The attainment of a desired formation of pores, and hence of a heat-insulating property, a lightness and a load-bearing strength being striven for, indeed even a volume being striven for, is therefore not guaranteed. Old glass has been employed for some time as a concrete aggregate. For this purpose, old glass is crushed so as to form glass-making sand. In Schweizer Ingenieur und Architekt, Issue No. 3 dated Jan. 18, 2000, the Begleitkommission SIA 162 (a Swiss commission promoting structural engineering) published xe2x80x9cBetonbautenxe2x80x9d (Concrete Structures), an opinion on the use of old glass as a sand substitute in concrete. In this article the risk is pointed out that, with reference to the alkali-silicate reaction, glass is an endangered aggregate and can react with the alkalis dissolved in the pore water of the concrete. This reaction results in voluminous reaction products which can lead to internal stresses and cracks and to the destruction of the concrete texture. It is further pointed out that materials very different from glass, such as lids (aluminium, lead) and labels etc, are crushed with the old glass and can lead to additional problems. Besides, it is pointed out in this communication that the bond between the cement matrix and the smooth surface of the glass grains is rather weak and that the use of glass can make later recycling of the concrete difficult. For this reason the use of glass as a sand substitute in constructional concrete is advised against by the Begleitkommission SIA 162 and by AG SIA 162-4 xe2x80x9cBetonxe2x80x9d (Concrete).
The object of the invention is therefore to create a flowable, setting compound with, in comparison with the state of the art, relevantly better and predeterminable properties with respect to weight per unit volume, compressive strength and/or thermal conductance. In particular, a constructional concrete with granulated lightweight aggregates is to be proposed that is suitable for building construction and civil engineering and capable of being cast on the building site in a formwork as cast-in-place concrete. Waste products or recycled primary material are to be capable of being used for the lightweight aggregates.
In accordance with the invention a flowable and settable casting compound with a binder and at least one lightweight aggregate is characterised in that the lightweight aggregate consists of crushed foam-glass lumps and, with the exception, if need be, of sand and still finer admixtures such as fillers, all the granulated aggregates consist of crushed foam glass.